The present invention relates to a fluid coupling device, and more particularly, to a type thereof for introducing a fluid into a rotary member rotated at high speed from a stationary side. The fluid coupling device is particularly available for applying a machining liquid into a gun drill of a machine tool.
One conventional fluid coupling device is shown in FIG. 1, using a contact type mechanical sealing system. In the device, a rotary shaft 53 formed with an axial fluid passage 54 is journalled by a coupling body 51 having generally cylindrical shape through bearings 52. The rotary shaft 53 has one planar end at which one end of the fluid passage 54 is opened. One end of the coupling body 51 is provided with a side member 51A formed with a fluid inlet port 55. A seat ring 57 formed with an axial fluid passage 56 is positioned so as to provide fluid communication between the fluid passage 54 of the rotary shaft 53 and the fluid inlet port 55. The seat ring 57 is movable in axial direction thereof is unrotatable about its axis by a pin 58 fixedly secured to the side member 51A. A coil spring 59 is provided between the side member 51A and the seat ring 57 to urge the seat ring 57 toward the planar end of the rotary shaft 53 (leftwardly in FIG. 1).
A follower ring 60 is fixedly coupled to the planar end of the rotary shaft 53. Therefore, one end face of the seat ring 57 is urged to be pressed toward the follower ring 60. Consequently, the follower ring 60 is hermetically slidingly rotated relative to the end face of the seat ring 57 so as to hermetically maintain fluid passing through the fluid passages 56 and 54.
With the above described conventional arrangement, since fluid coupling is maintained by the mechanical seal system in which the follower ring 60 is in facial sliding contact with the end face of the seat ring 57, rotation speed of the rotary shaft 53 should be within a low level, otherwise frictional wearing may occur at the interfaces of the follower ring and the seat ring. If the applied fluid has high pressure or high temperature, high sealing performance at that portion must be required. To this effect, biasing force of the coil spring 59 must be increased. Accordingly, rotational speed of the rotation shaft 53 must be lowered to avoid frictional wearing. In summary, the mechanical seal type fluid coupling device is not available for the high speed rotation of the rotary shaft 53.
Further, the mechanical seal type fluid coupling device cannot perform idle rotation of the rotary shaft 53 so as to protect the sliding surfaces of the follower ring 60 and the seat ring 57. Moreover, a filter unit is required to avoid entry of the high hardness particles into the fluid passage when applying the liquid thereinto, otherwise the high hardness particles may damage the sliding surfaces.
Another type of conventional fluid coupling device is described in Japanese Utility Model Application (Kokai) No. 57-166644. This device is of non-contact type fluid coupling device as shown in FIG. 2, in which a minute hollow space or gap is defined between an inner peripheral surface of a coupling body 71 and an outer peripheral surface of a rotary shaft 72 rotatably extending through the coupling body 71 through bearings 75. The rotary shaft 72 is formed with an axial oil passage 74. The minute gap 73 has a radial gap of about 0.02 mm so as to seal a machining liquid passing through the oil passage 74.
In the conventional non-contact type fluid coupling device, the rotary shaft 72 can be rotated at high speed. However, if the applied fluid has high pressure, fluid leakage may occur, so that the leaked machining liquid may enter the bearings 75 to degrade their inherent function. Further, no system is provided in the conventional device for processing the leaked fluid. Therefore, aqueous machining liquid or pure water cannot be employed as the machining liquid passing through the fluid passage 74, since they may lead to corrosion of the device.